Reporter: In broad daylight, in the middle of the night. There are a million ways to die. But the criminal justice system really only concerns itself with one -- homicide. That's what the thomas family of alabama suspects happened in the mystifying death of shirley seitz. They accuse shirley's husband, dr. Mike wohlschlaeger. I intend to see that he's dealt with. And he can take that to the bank. Reporter: A flicker of suspicion about what happened in the house on camelot court is now a raging five-alarm mission for what they see as justice that has fully engulfed three generations of the thomas family and leads to two more of dr. Mike's five wives. So, I just get on the internet and start facebooking. Reporter: Relentless, sharon has tracked down yet another wife. Number three, gloria potts. And I said, "well, I would like to talk to her. I just want to find out, who is this person that we thought we knew?" Reporter: Gloria says she knows things about dr. Mike. Hey. Give me a hug. Reporter:20/20" was there when gloria met shirley's family face-to-face for the first time. What could have been the most awkward family reunion ever, relatives of the fifth wife meeting the third wife. It's the dr. Mike ex-wives club. Bonding over their shared suspicion. It's so good to meet all of y'all, to be able to let y'all know how I feel and that I'm so sorry. Reporter: Of course, mike is missing. And so is shirley. I didn't know shirley, but it was almost like I had lost someone. Reporter: Gloria spoke with sharon by phone soon after shirley's death. She believes that toward the end of their marriage, michael was trying to poison her. I felt like I was being poisoned. I really did. Reporter: You got sick? Sick, couldn't hardly move. And then that's when I turned around and told her, "gloria, i can't believe you're saying this to me," but I said, "mother has had the same symptoms." Reporter: The family of wife number five, shirley, wondered if dr. Mike had been trying to poison her, too. And you guessed it, here comes mrs. Wohlschlaeger number four -- diana. Today's date is february the 4th, 2011. Reporter: In a recording obtained by "20/20," investigators question diana yohn, the fourth stop on dr. Mike's matrimonial trail. The wife between gloria and shirley. I think the man's dangerous, personally. Do you think that he is capable of murder? I don't know. Reporter: She has no proof, but diana tells police toward the end of her their marriage, when she had a $250,000 life insurance policy, she suspects dr. Mike may have been trying to poison her, too. You think he may have been giving you some type of medication but you're actually not sure of that? Yeah. I mean, it just seems my headaches were so bad, and I get migraine headaches, okay? And it's documented that I do. But they were so bad when i lived with him, I couldn't even work, I could hardly function. Reporter: Near the end of her a chilling request. And I'll be honest with you. If something happens to me, he needs to be investigated. Reporter: So now two more wives suspect dr. Mike was trying to poison them, and one of them says hold on, that's not all. Wife number three, gloria, revealed a terrible trauma she says happened in her marriage nearly 30 years ago. She says dr. Mike, the man who had always killed her with kindness, tried to kill her with a mallet. And I was asleep, and he hit me in the back of the head with a mallet. Reporter: With a mallet? Yes. And all of a sudden, a pillow went over my face and his hand came under the pillow and covered my nose and my mouth. Reporter: Gloria says she escaped by playing dead, and then running out of the house. I was hysterical, crying and upset. And when I would try to yell for help, I'd go -- "help, help!" And I had no voice. Reporter: You went to the hospital? I went to the hospital, but we told them I slipped in the tub. Reporter: Did you ever ask him at any point, "why were you doing that, why did you try to kill me?" Yes. He told me he had gotten stung by a jellyfish when he worked in china, and that it was a reaction to the toxins. Reporter: That's right, she says dr. Mike's excuse for hitting her over the head with a mallet? The jellyfish made him do it. Had there been an argument or something? No. Reporter: So it was just this one time. Just this one time, he snapped. Reporter: Gloria says she told no one, not even the police. Sticking to the story of slipping in the tub until she and mike divorc, about ten years later. Only then, she says, did she begin telling people. She also got a restraining order. So people are going to wonder, okay, so you get hit over the head -- the guy puts a pillow over your head and you didn't goft hdivorce him right then. You stayed. Yes. Reporter: Have you asked yourself why? A million times, I can't understand why. I have no answer to that question. I'm sorry that I didn't -- it's all right. I told you that. I really should have called. Reporter: She says she had two children to think of. And aside from the one incident, mike was never violent. So besides the fact that he hits you with a mallet, he was a good husband? Other than trying to kill me, to my knowledge, he was a very good husband. It doesn't make sense. And me staying didn't make sense. Reporter: Maybe she's just mad. Maybe she is trying to get back at him. Possible. That's a possibility. But she had been telling the same story for a number of years. It didn't just come up after shirley died. Reporter: Can you still see him standing over you? Yes. And I was -- I was terrified. I didn't know what to do. Reporter: Now, remember, when gloria told the family and then police this amazing tale of mike's alleged attack, no one knew what killed shirley. The autopsy was not finished yet. So, imagine the reaction when, months later, the family is finally given the results. I'm shaking my head. I can't believe this. I cannot believe this. I can't believe this is happening. Reporter: Why? Because the medical examiner finds what caused shirley's death is no migraine. It's a blow to the head. "Blunt force head injuries." A hit to the back of the shirley's skull, hard. That is what killed her. So, when you find out, later on, that it's blunt force trauma to the head -- oh. Then there's no question in my mind. That michael murdered this woman, murdered shirley. My mother has actually been killed. This man has killed my mama. Reporter: But not so fast. The toxicology report found no poison or fatal doses of drugs. And even as it makes clear the cause of death, the autopsy fails to answer the really big question -- the manner of death, how shirley got that fatal injury. The medical examiner writes simply "undetermined." Accident? Homicide? Can't tell.

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